Development and utilization of assays for monitoring cell mediated and humoral immunity in the mouse to type C virus and type C viral antigens and non-viral antigens in cellular vaccines prepared from syngeneic tumor cell lines. Determination of the optimal production, fixation, handling and storage of inactivated type C virus vaccines for maintenance of immunogenicity. Determination of the immunogenicity and oncognicity of naturally occurring, live type C virus used as a vaccine in adult laboratory animals. Determination of whether type C virus vaccines can prevent spontaneous tumors in mice known to have measurable humoral and cellular immune responsiveness to the viral immunogens. Determination of the immune competence of laboratory animals with aging and with development of naturally occurring neoplasms and the effect of transfer of syngeneic immunocompetent cells on the incidence of naturally occurring neoplasms.